According to German law at the time, presumably, they were not committing murder. It's hard to say because it's entire possible for members of a country's military to follow illegal orders and be breaking the law.
According to international law, they were committing murder.
Murder is defined as illegal homicide. As such, it can only be really be discussed in the context of a legal framework. But there can be many legal frameworks at play in any one place/instance.
I'm saying there is a moral framework that supersedes a legal one, and I reject the "dictionary.com" definition as the conical definition.
From the Oxford dictionary, there is more to the meaning than your shallow lawful vs unlawful demarcation line:
. a. The most heinous kind of criminal homicide; also, an instance of this. In English (also Sc. and U.S.) Law, defined as the unlawful killing of a human being with malice aforethought; often more explicitly wilful murder.
In OE. the word could be applied to any homicide that was strongly reprobated (it had also the senses ‘great wickedness’, ‘deadly injury’, ‘torment’). More strictly, however, it denoted secret murder, which in Germanic antiquity was alone regarded as (in the modern sense) a crime, open homicide being considered a private wrong calling for blood-revenge or compensation. Even under Edward I, Britton explains the AF. murdre only as felonious homicide of which both the perpetrator and the victim are unidentified. The ‘malice aforethought’ which enters into the legal definition of murder, does not (as now interpreted) admit of any summary definition. Until the Homicide Act of 1957, a person might even be guilty of ‘wilful murder’ without intending the death of the victim, as when death resulted from an unlawful act which the doer knew to be likely to cause the death of some one, or from injuries inflicted to facilitate the commission of certain offences. By this act, ‘murder’ was extended to include death resulting from an intention to cause grievous bodily harm. It is essential to ‘murder’ that the perpetrator be of sound mind, and (in England, though not in Scotland) that death should ensue within a year and a day after the act presumed to have caused it. In British law no degrees of guilt are recognized in murder; in the U.S. the law distinguishes ‘murder in the first degree’ (where there are no mitigating circumstances) and ‘murder in the second degree’ (though this distinction does not obtain in all States).
